Digital still cameras and digital video cameras that have become increasingly popular in recent years convert an image signal, which is the result of sensing an image by an image sensing device such as a CCD sensor, to image data in a digital format and store this image data on a recording medium such as a memory card.
Such digital image data can readily be corrected, manipulated and printed by a computer and has come to be utilized in the ordinary home. At the same time, owing to the spread of networks, particularly the Internet, it is now easy for digital image data to be circulated among an unspecified number of users.
Against this background, the necessity for imaging apparatus such as digital still cameras and digital video cameras has grown explosively.
The widespread use of personal computers and the like has made the copying of digital data easier and less expensive. In addition, easier access to the Internet has facilitated and lowered the cost of distributing digital data. As a consequence, even ordinary individuals can now create and distribute copies of digital images easily and inexpensively for purposes beyond private use. Though acts such as the unauthorized copying and distribution of digital image data do not pose a major problem so long as it involves photography for personal enjoyment, such behavior has not gone unnoticed by those who circulate digital images as a business.
Thus, a problem which arises with regard to image data in digital form is that protection of the copyright of photographers, etc., is not satisfactory. Means for protecting copyright is strongly desired for digital image data obtained by photography.
A technique referred to as an “electronic watermark” has undergone extensive research for the purpose of realizing copyright protection of digital image data. This technique is one in which a portion of the data in digital image data or digital audio data is embedded with separate information by superposition in such a manner that the information is rendered insensible or intentionally sensible to a human being, depending upon the particular purpose. When necessary, only a user having the right or qualifications can extract or remove the embedded separate information from the digital data in which the electronic watermark has been embedded.
For the details of these techniques, see the specifications of Japanese Patent Application Laid-Open Nos. 10-290359 and 10-150517 and U.S. Pat. No. 5,530,759 (Japanese Patent Application Laid-Open No. 8-241403)
A number of methods have generally been employed for authenticating individuals. Examples are a method through which only a specific person is verified by a key, card or seal in his or her possession, and a method through which only a specific person is verified by entry of a password number known only by the person. A fundamental problem with this method is that it is comparatively easy for another person to pose as the specific person by way of theft, counterfeiting or leakage of information, etc.
Accordingly, a method that has become the focus of attention as an alternative to the above method is a biometric personal authentication method that employs a physical characteristic of a specific person to undergo authentication.
It is required that a physical characteristic be unique and person-specific, exhibit randomness and not change over a long period of time. In addition, when application to an apparatus for performing personal authentication is taken into account, facts to be considered are the time needed to acquire the data needed for authentication and the cost of the apparatus. At the present time, therefore fingerprints, palm prints, iris patterns, voice prints and facial appearance are in wide use as physical characteristics for use in authentication.
Japanese Patent Publication No. 8-504979 (Japanese translation of PCT International Publication WO94/09446) will be described in general terms with regard to the principle of personal authentication using an iris pattern.
FIG. 9 is a flowchart of processing up to a decision as to whether a person being tested is a specific individual or not.
First, the eyeball image of the person is acquired by controlling illumination and focus (1101). When the eyeball image is obtained, the eyelid and eyelash are detected, the pupil-iris boundary 21 and outer boundary 22 of the iris are detected, as shown in FIG. 10, and a coordinate system is set up upon dividing the eyeball into areas 23 referred to as analysis bands (1102).
Next, image analysis (1103), which mainly entails extracting a change in shading of the analysis bands, is performed, and coding is performed based upon the result of analysis (1104). The personal authentication code generated by coding is expressed by a fixed-length stream of bits indicated by “1”s and “0”s.
Matching is performed (1105) between the personal authentication code thus obtained by acquiring the iris pattern and coding the same and a personal authentication code 1107 serving as a template previously acquired from the specific individual and stored. More specifically, the degree of agreement between the two codes is calculated in accordance with a certain evaluation function and, if an evaluation value exceeds a fixed threshold value, it is decided that the two codes are personal authentication codes sampled from the same individual (1106).
Further, if a fingerprint or palm print is used for personal authentication, the image of the fingerprint or palm print of the person to be authenticated is acquired, the image is coded based upon ridge endings or ridge bifurcations, which are the minutia of the ridges that constitute the fingerprint or palm print, and matching is performed with a previously stored template through a procedure similar to that in the case of the iris pattern, thereby achieving personal authentication.
The specification of Japanese Patent Application Laid-Open No. 2000-196998 discloses a method that uses the above-described technique to embed eye information in a photographic image directly as a watermark.
In accordance with this method, an eyeball image is acquired at substantially the same time the image of a subject is taken by a camera, an iris pattern or retinal pattern is extracted from the eyeball image, and the extracted image or code based upon the image is embedded in the photographic image as photographer information. As a result, the photographic image and the photographer information are placed in one-to-one correspondence and there is no way for a third party to intervene. The embedded photographer information therefore is highly reliable as copyright information.
However, the above method necessitates the task of acquiring the eyeball image at approximately the same time that the image of the subject is taken. There are also cases where the method necessitates the additional task of extracting the iris pattern or retinal pattern from the eyeball image and converting this pattern to a personal authentication code by coding means that relies upon image processing. In a digital image sensing device such as a digital still camera, such a task is carried out, in terms of the processing sequence, at the timing at which maximum load is imposed upon processing of the subject image at the time of photography. When eyeball-image processing is executed along with processing of a captured image, therefore, the overall processing requires a great amount of time. This means that the photographer must wait a while before these processes are completed and the next photo can be taken, resulting in possible loss of photographic opportunities.
When the eyeball image of a photographer is acquired every time an image is taken, the photographer's eye may be closed at the moment of acquisition or an eyelash or strand of hair may interfere. In view of the fact that this can happen frequently, the eyeball image may not always be acquired properly. Furthermore, since the pupil of the photographer's eye opens when an image is taken under low illumination, as is the case indoors, the area of the iris pattern becomes comparatively small and it may not be possible to convert the pattern to an accurate personal authentication code.
Accordingly, the method of acquiring iris information at the same time that a subject is photographed is disadvantageous in view of the heavy processing load and involves the risk that authentication precision may be influenced by circumstances.
On the other hand, in order to record biological information of a photographer in a captured image without acquiring the biological information at the same time that the subject is photographed, it is necessary that the photographer register his/her own biological information in the imaging apparatus beforehand by some method. Repeating the registration operation with each use is very troublesome for the photographer. However, if the biological information is not updated with each use, the biological information registered initially will be recorded even in image data captured by another photographer sharing the same imaging apparatus. If this happens, it will not be possible to achieve the objective of recording copyright-related information while linking a photographic image and its photographer by biological information embedded in image data.